The invention relates to antibodies, and antigen binding fragments thereof, that neutralize infection of both group A and group B Respiratory Syncytial Virus (RSV). The invention also relates to antigenic sites to which the antibodies and antigen binding fragments bind, as well as to nucleic acids that encode and immortalized B cells and cultured plasma cells that produce such antibodies and antibody fragments. In addition, the invention relates to the use of the antibodies, antibody fragments, and polypeptides recognized by the antibodies of the invention in screening methods as well as in the diagnosis, treatment and prevention of RSV infection and group A and group B RSV co-infection.
Respiratory Syncytial Virus (RSV) is a common cold virus that belongs to the family of paramixoviruses. The virion of RSV is enveloped with a lipid bilayer, which contains glycoproteins including the attachment protein G and the fusion protein F. RSV strains are separated into two major groups (A and B) on the basis of antigenic and genetic variability. The amino acid sequences of the G and F proteins of RSV are classified into A and B groups. The F protein of RSV is a type I trans-membrane surface protein that has an N-terminal cleaved signal peptide and a membrane anchor near the C-terminus. The F protein is synthesized as an inactive F0 precursor that assembles into homotrimers and is activated by cleavage. The F protein is formed by three domains (DI to DIII), a fusion peptide (FP) and three heptad-repeats regions (HR-A, -B and -C). The F glycoprotein of RSV directs viral penetration by fusion between the virion envelope and the host cell plasma membrane. The N-terminus of the F subunit, that is created by proteolytic cleavage and contains the fusion peptide, inserts directly into the target membrane to initiate fusion. After binding to the target cell and subsequent activation, the metastable pre-fusion F protein undergoes a series of structural rearrangements that result in the insertion of the fusion peptide into the target cell membrane, followed by the formation of a stable helical bundle that forms as the viral and cell membranes are apposed. These structural changes lead to the formation of a stable post-fusion F protein. Later in infection, the F protein expressed on the cell surface of infected cells can mediate fusion with adjacent non-infected cells forming large syncytia.
Respiratory Syncytial Virus (RSV) is the most common cause of lower respiratory tract disease in children less than two years. It is also the cause of severe disease in premature newborns, hospitalized children (Hall, C. B. et al., 2009, N Engl J Med 360, 588-598), immune-compromised patients (Falsey, A. R. et al., 2005, N Engl J Med 352, 1749-1759), and patients with chronic lung disease and congenital heart disease. RSV plays a role in acute asthma exacerbations (Edwards, M. R. et al., 2012, Nat Rev Immunol 10, 459-471) and is also a cause of acute respiratory tract illness in lung transplant recipients leading to increased risk of chronic rejection.
Immunocompromised patients have a 5% to 15% rate of RSV infection and the progression to low respiratory tract infection (LRTI) is observed in 38% of these patients with an average mortality of 32%. There is no effective treatments to prevent the spread of the virus or to control LRTI. Ribavirin and IVIG have been used with limited success. Immunity to RSV appears to be short-lived, and thus re-infections are frequent (Ogra, 2003, Paediatric Respiratory Reviews 5 Suppl A: S119-126).
Vaccines for RSV infection are currently not available. A formalin-inactivated and alum-adjuvanted RSV vaccine (FI-RSV) tested in the 1960s was found to predispose infants for enhanced disease following natural RSV infection leading to high fever and severe pneumonia, resulting in high hospitalization rates and even some fatalities (Fulginiti et al., 1969, American Journal of Epidemiology 89:435-448; Kapikian et al., 1969, American Journal of Epidemiology 89:405-421; Kim et al., 1969, American Journal of Epidemiology 89:422-434).
Evidence for the role of serum antibodies in protection against RSV virus has emerged from epidemiological as well as animal studies. In infants, titers of maternally transmitted antibodies correlate with resistance to serious disease (Glezen et al., 1981, The Journal of Pediatrics 98:708-715) and in adults incidence and severity of lower respiratory tract involvement is diminished in the presence of high levels of serum RSV neutralizing antibodies (McIntosh et al., 1978, The Journal of Infectious Diseases 138:24-32).
A monoclonal antibody, palivizumab (SYNAGIS®), is registered for the prevention of RSV infection in premature newborns. In addition to palivizumab, other monoclonal antibodies shown to neutralize RSV infection, such as 101F and D25, as disclosed in EP 1 997 830 A1, have also been described. The antibody registered for the prevention of RSV infection, palivizumab, is, however, not potent and the response to palivizumab is varied among individuals. Further, it fails to prevent RSV infections effectively in some cases (Weisman, L. E., 2005, Curr. Opin. Mol. Ther. 11, 208-218) and prolonged pulmonary replication of RSV in the presence of palivizumab is followed in animals by the appearance of resistant virus strains (Zhao and Sullender, 2005, Journal of Virology 79:3962-3968).
Accordingly, there is still a need for agents capable of preventing as well as treating or attenuating RSV infection in high-risk patients with high potency and efficacy. Further, it is important to have antibodies that target different epitopes and different antigenic sites on the various strains in order to avoid appearance of resistant virus strains.